This invention relates to pressure transmitters for use in the production of composite components. The term xe2x80x9cpressure transmitterxe2x80x9d as used herein is intended to refer to cover members and ancillaries used to allow pressure to be applied to composite components during their moulding in a tool. The expression includes caul plates, pressure intensifiers and reusable rubber bags.
The use of caul plates, pressure intensifiers and rubber bags to produce smooth surfaces on composite components is a normal practice. Caul plates and/or pressure intensifiers can be made from an elastomeric material and enable appropriate pressure to be applied to the laminate in order to provide a relatively smooth surface on the bag side. In the case of pressure intensifiers, these are mainly used in female features on the non moulded side of the component. The caul plates consist of an elastomeric sheet which may be reinforced by a resin pre-impregnated fibre. The disadvantage of these caul plates made from fully formulated sheet rubber is that they require to be cured at high temperatures (greater than 100xc2x0 C.). Also, some reinforced caul plates exhibit the disadvantage that the elastomeric material tends to separate from the fibre reinforcement, and others may give undesirable contamination problems.
As used herein, the expression xe2x80x9cpartially curedxe2x80x9d when referring to a curable component means cured to the extent that the component can be removed from a mould, tool or former (which may or may not have high temperature capability (ie being capable of withstanding temperatures of greater than 100xc2x0 C.)), and then be handled and further processed (including a higher temperature further curing stage) without causing damage to the component. Further the expression xe2x80x9celastomeric materialxe2x80x9d includes the precursors of such materials, for example, fully formulated polymeric materials which after partial or full cure exhibit elastomeric properties. The polymeric material may be in sheet form.
According to a first aspect of the present invention there is provided a pressure transmitter comprising an elastomeric material which is partially or at least partially cured at a temperature not exceeding 100xc2x0 C.
According to a second aspect of this invention, there is provided a pressure transmitter for use in the production of composite components, the pressure transmitter comprising an inner region of a reinforcement and an outer region of an elastomeric material, the elastomeric material being partially or, at least partially, curable at a temperature not exceeding 100xc2x0 C.
Preferably, the elastomeric material is partially or, at least partially, curable at 20-70xc2x0 C., preferably 65xc2x0 C. Conveniently the elastomeric material is partially cured during a period of 14 hours.
Desirably, the elastomeric material is further cured at an elevated temperature to reach a state of being substantially fully cured. Preferably the elevated temperature lies in the range 170-185xc2x0 C. Preferably, the elastomeric material can be further cured at a temperature of substantially 175xc2x0 C. Conveniently the elastomeric material is further cured for a period of at least 2 hours.
Preferably elastomeric material is a silicone elastomer, an acrylate or a fluoroelastomer.
According to a further aspect of this invention, there is provided a pressure transmitter for use in the production of composite components, the pressure transmitter comprising an inner region of a curable reinforcement and an outer region of elastomeric material, the curable reinforcement comprising resin pre-impregnated onto fibres, said resin being partially, or at least partially, curable at 100xc2x0 C. or less.
Preferably the elastomeric material cures or at least partially cures at a temperature greater than the cure or partial cure temperature of the curable reinforcement. This provides the advantage that the resin cures or partially cures before the elastomer, thereby reducing shrinkage of the elastomer.
Preferably, the elastomeric material is partially, or at least partially, cured at a temperature in the range of 20-70xc2x0 C. more preferably at 65xc2x0 C. Preferably, the elastomeric material is partially cured during a period of 14 hours.
Desirably the elastomeric material is further cured to reach a state of full cure at a temperature in the range of 170-185xc2x0 C. Preferably, the elastomeric material can be further cured at a temperature of substantially 175xc2x0 C. Conveniently the elastomeric material is further cured during a period of 2 hours.
According to a still further aspect of this invention, there is provided a pressure transmitter for use in the production of composite components, the pressure transmitter comprising an inner region of a curable prepreg reinforcement and an outer region of an elastomeric material, the curable prepreg reinforcement being in the for m of resin pre-impregnated fibres defining a plurality of interstitial spaces, wherein the elastomeric material of the outer region substantially fills the interstitial spaces.
This has the advantage that the elastomer is keyed to the fibres, thereby mitigating any separation of the resin pre-impregnated fibres from the elastomer.
Preferably, the pressure transmitter is in the form of a caul plate, or a pressure intensifier for use in applying pressure to surfaces of a moulded component. The invention is particularly suitable for use with moulding techniques which involve the use of a bag applied to the moulding, for example by using vacuum bags.
According to another aspect of this invention, there is provided a method of curing a pressure transmitter, comprising providing a pressure transmitter as described above, and thereafter at least partially curing the pressure transmitter at a temperature not exceeding 100xc2x0 C.
The pressure transmitter may be partially or, at least partially, cured at a temperature in the range of 60-70xc2x0 C. (approximately 140-160xc2x0 F.), more preferably at 65xc2x0 C. (approximately 150xc2x0 F.). Conveniently, the pressure transmitter is partially cured during a period of at least substantially 14 hours. The pressure transmitter may be partially cured within 14 hours.
Desirably, after said partial or, at least partial, curing, the pressure transmitter is further cured at a temperature in the range of 170-185xc2x0 C. (approximately 340-365xc2x0 F.). Preferably, the pressure transmitter is further cured at a temperature of substantially 175xc2x0 C. (approximately 350xc2x0 F.). The pressure transmitter may be so further cured during a period of at least substantially 2 hours. The pressure transmitter may be so further cured within 2 hours.
The elastomeric material may be a silicone elastomer.
By appropriate selection of the resin and elastomeric material, the low temperature curing of the pressure transmitter will result in the resin curing or, partially curing, before the elastomer has fully cured. This has the advantage of minimising shrinkage of the elastomer. Another advantage of the low temperature curing (ie less than 100xc2x0 C.) is that it can take place on a tool that can only withstand such low temperatures. The step of further curing the pressure transmitter provides the elastomeric material with the properties to enable the pressure transmitter to perform its function.